Propargylic and allenic organometallics are of great interest, because they process tremendous potential in synthetic organic chemistry. For a review of these types of compounds and their many uses in synthetic organic chemistry, see J.-L. Moreau in "The Chemistry of Ketenes, Allenes and Related Compounds", ed. S. Patai, J. Wiley, New York, 1980, pp. 363-414, which is incorporated by reference. For other similar references see H. Hiemstra and W. Nico Speckamp, Tetrahedron Lett., 1983, 23, 1407; N. R. Pearson, G. Hahn and G. Zweifel, J. Org. Chem., 1982, 47, 3364; C. Huynh and G. Linstrumelle, J. Chem. Soc., Chem. Commun., 1983, 1133; M. Ishiguro, N. Ikeda and H. Yamamoto, J. Org. Chem., 1982, 47, 2225; C. J. Elsevier, H. Kleijn, K. Ruitenberg and P. Vermeer, J. Chem. Soc., Chem. Commun., 1983, 1529, all of which disclosures are incorporated in the background herein by reference. The major problem with these compounds heretofore has been their tendency to equilibrate (equation 1) or to react so as to ##STR1## give mixtures of allenic and propargylic products.
The brominaton (pyridinium hydrobromide perbomide), iodination (iodine) and acylation (RCOCl/AlCl.sub.3, -20.degree. C., CH.sub.2 Cl.sub.2) of allenic and propargylic organomercurials proceeds with rearrangement to afford higher yields of the corresponding propargylic and allenic bromides, iodides and ketones, respectively.
It has now been found that if one reacts propargylic halides and metallic mercury to provide the corresponding allenic or proparaglic organomercurials, the tendency to equilibrate and to give mixtures of products can be eliminated making the corresponding allenic and propargylic organomercurials highly useful intermediates. This is particularly surprising in view of the teachings of the prior art.
Only one propargylic and one allenic organomercurial are known to have been reported in the literature previously, see M. Gaudemar, Bull. Soc. Chim. France, 1962, 974. These compounds were prepared from the corresponding organozinc reagents, thus limiting the types of functional groups which might be accommodated. In 1884, L. Henry, Ber. Dt. Chem., Ges., 1884, 17, 1132 reported that the reaction of propargyl iodide and metallic mercury in sunlight gives propargyl mercuric iodide (eq. 2). This approach to the desired organomercurials ##STR2## appeared attractive, particularly since it would appear to accommodate a wide range of organic functionality. The reported process of the Henry article has surprisingly been found to be in error. One cannot prepare propargyl mercuric iodide by the process suggested by Henry. Instead, it has surprisingly been found that where a terminal alkyne such as reported by Henry is used in the reaction process in every instance the compound synthesized is an allenic mercurial.
Accordingly, a primary objective of the present invention is to provide a convenient, predictable and selective synthetic route for preparing, at the process operator's wishes, either allenic or propargylic organomercuric halides in high yield.
Yet another objective of the present invention is to prepare, in a single step synthesis reaction, either propargylic or allenic mercuric halides alone, without mixtures of both being present, such that they can selectively be used as synthesis precursors in types of reactions earlier mentioned in the incorporated literature references.
An even further objective of the present invention is to provide a highly convenient route to a variety of allenic and propargylic organomercuric halides in high yields which are readily isolatable for use in further processing reactions.
The method and manner of accomplishing each of the above objectives as well as others will become apparent from the detailed description which will follow hereinafter.